The polypeptides of structure (I) wherein Asp, Pyr-Glu, Pyr-Gln-Asp and so on are abbreviations, very familiar to those skilled in polypeptide chemistry, indicating amino-acid, dipeptide and tripeptide residues, are known in the literature and the various methods of preparation are described in details therein, see for instance German Pat. No. 1,643,504, British Pat. No. 1,523,038, U.S. Pat. No. 3,705,140, U.S. Pat. Nos. 3,723,406; 3,734,946; 3,839,315.
Some of polypeptides of structure (I) are not covered by the above mentioned patents, such as phyllocaerulein, and Asn.sup.2, Leu.sup.5 -caerulein which are described in papers cited hereinbelow: ##STR2## "Structure and pharmacological actions of phyllocaerulein, a caerulein-like nonapeptide: its occurrence in extracts of the skin of phyllomedusa sauvagei and related phyllomedusa species". A. Anastasi, G. Bertaccini, J. M. Cei, G. de Car, V. Erspamer and M. Impicciatore, Brit. J. Pharmacol. 37, 198-206 (1969). "Synthesis of phyllocaerulein", L. Bernardi, G. Bosisio, R. de Castiglione and O. Goffredo, Experientia, 25, 7-8 (1969). ##STR3## "Occurrence of Asn.sup.2, Leu.sup.5 -caerulein in the skin of the African frog Hylambates maculatus", C. Montecucchi, G. Falconieri, V. Erspamer and J. Visser, Experientia, 33, 1138-1139 (1977).
All these polypeptides possess cholecystokinin activity and are generically active also on the gastro-intestinal tract. One of the most intensively experimented polypeptides of this class is ceruletide, generic name for a decapeptide having the structure: ##STR4##
This decapeptide, its chemico-physical, pharmacological properties as well as the detailed preparation are described in U.S. Pat. No. 3,472,832 and in the equivalent foreign patents, among which we quote British Pat. No. 1,146,800 and German Pat. No. 1,643,504 where ceruletide is claimed per se.
Ceruletide is in particular indicated for adjunctive use in cholecystography as it induces contraction of the gallbladder with consequent evacuation of radioopaque bile into the bile ducts.